The present invention relates to a press die system for forming clamshell container assemblies from a sheet of material by simultaneously forming the top portion in one blank of sheet material and the bottom portion in an adjacent blank of sheet material. More particularly, the present invention relates to an apparatus and method for progressively forming clamshell assemblies having two interconnected container portions such that the equivalent of the whole assembly is produced for each single stroke of a male die means.
Clamshell containers for temporarily storing food items, such as various types of sandwiches, are well known. The clamshell container assembly generally has a top portion or lid and a bottom portion that are interconnected by a connecting portion or hinge. By packaging an individual sandwich in this type of clamshell assembly, the sandwich is insulated somewhat to maintain a serving temperature, and is further protected from any contamination or damage from external sources. In addition, the clamshell container may serve as a convenient serving item for the sandwich, and may display graphics identifying the specific food item.
It has been common practice in the food industry to utilize clamshell container assemblies formed from synthetic materials such as expanded polystyrene. However, demand for expanded polystyrene clamshell container assemblies is falling because of environmental concerns related to the use of expanded polystyrene, and particularly to the well-known disposability problems affecting containers formed from expanded polystyrene.
Paperboard is an alternative material that provides a suitable replacement for expanded polystyrene in the manufacture of clamshell container assemblies. Significantly fewer environmental problems are associated with its manufacture and disposal. Additional advantages of paperboard clamshell assemblies in comparison to assemblies made of synthetic materials include improved printability and wider consumer acceptance. However, the inability to form easily and quickly a clamshell container assembly from paper stock has been a barrier to the development and use of paperboard in the clamshell container-forming industry.
One problem with conventional machines for forming paperboard clamshell containers is that it has been necessary to form each container portion of a clamshell assembly separately because of known problems related to drawing and forming the paperboard during the forming process. A description of some of these problems is included in U.S. Pat. No. 4,637,811 to Fortney.
A two-step process of converting a single blank of sheet material to form two interconnected clamshell assembly portions was generally required to address the above-noted problems. By requiring two sequential and separate forming strokes of the press machine, the time, and consequently the cost, of producing paperboard clamshell assemblies has retarded the acceptance of such paperboard clamshell assemblies in the industry.
Another problem with machines for forming paperboard clamshell assemblies is that such machines have been unable to form a skirt on one of the clamshell container portions. A skirt is desirable becuse it forms an overlapping closure when the two container portions are mated to form the assembled clamshell.
One object of the present invention is to provide a press die machine that is able to convert paperboard or other sheet material into clamshell container assemblies or the like quickly in an improved manner to avoid tearing the common hinge region interconnecting the container portions. In particular, a press die machine capable of producing the equivalent of a completed paperboard clamshell assembly for each individual stroke of the machine is desired to speed up container manufacturing rates.
Another object of the present invention is to provide a press die machine that is capable of forming a container closure skirt around one of the clamshell container portions.
According to the present invention, a die machine is provided for progressively forming a clamshell container assembly from a paperboard blank having leading and trailing portions. The die machine includes female die means, male die means, and press means for providing relative movement between the male and female die means. The female die means is formed to include first and second mold cavities. The male die means includes a first die for engaging the first mold cavity to establish a first pressing station and a second die for engaging the second mold cavity to establish a second pressing station.
First stop means is included for selectively blocking moement of a blank relative to the female die means to position a leading portion of the blank at the first pressing station so that one container portion of the clamshell assembly is formable in the first mold cavity upon mating engagement of the female and male die means during a first pressing operation. Shift means is provided for selectively moving the leading portion of the blank relative to the female die means to simultaneously conduct the leading portion of the blank past the second pressing station and the trailing portion of the blank past the first pressing station. Second stop means is provided for engaging the partially formed blank following operation of the shift means to position the trailing portion of the partially formed blank at the second pressing station so that the remaining container portion of the clamshell assembly is formable in the second mold cavity upon mating engagement with the male and female die means during a subsequent pressing operation.
In use, the first stop means positions the first blank in a proper position relative to the first mold cavity and the first male die such that one of the container portions of the clamshell assembly is formed from the leading portion of the blank when the first male die is moved into engagement with the first mold cavity during a first pressing operation. Following the first pressing operation, the shift means is activated and acts to move the completed first container portion out of the first mold cavity and to position the blank, and specifically the trailing portion of the blank, over the second mold cavity. The second stop means acts to position the trailing portion of the blank over the second mold cavity properly to permit the second mold cavity and second male die to form a second container portion upon engagement of the second male die with the second mold cavity during a second pressing operation.
As the trailing portion of the above-described first blank is being formed into the second container portion, a leading portion of a subsequent, second blank is simultaneously introduced into the machine and positioned in the first pressing station to permit formation of a first container portion of that second blank. Thus, during one downstroke of the male die means in the die machine, the equivalent of one clamshell assembly is completed by this simultaneous forming of the second container portion of the first blank and the first container portion of the spaced-apart, adjacent second blank.
One advantage of the foregoing structure is that the die machine of the present invention is capable of forming paperboard clamshell assemblies such that the equivalent of one completed assembly is produced for each stroke of the machine. In addition, during a single stroke of the press machine, only one container portion in each of a first and second blanks is being formed. One advantage of this feature is that, although the press machine is capable of producing the equivalent of a completed clamshell assembly for each stroke of the machine, the machine is nevertheless capable of producing interconnected container portions without the above-described paperboard drawing and forming problems that would normally be associated with simultaneously forming both container portions of the same blank.
In preferred embodiments of the present invention, the female die means is inclined with respect to a horizontal plane to cause a series of separate blanks to move by gravity through the die machine. In addition, the shift means includes ejector means for simultaneously ejecting blanks from the first and second mold cavities so that a blank ejected from the first mold cavity moves by gravity toward the second mold cavity.
One feature of the foregoing structure is that, because of the inclined orientation of the female die means, gravity is utilized to move the blanks over the first and second mold cavities and between the first and second pressing stations. One advantage of this feature is that no additional structure is necessary to move the blanks between the first and second pressing stations, which reduces the complexity of the machine, and increases its efficiency.
Thus, the press machine of the present invention is capable of producing the equivalent of a completed clamshell assembly with each stroke of the press machine dies. However, because of the progressive forming steps of the machine, problems normally associated with forming adjoining container portions from paperboard with one stroke of a press machine are eliminated.
Additional objects, features, and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.